The effectiveness of persulfate oxidation for the destruction of tetrachlorobiphenyl a representative polychlorobiphenyl (PCB), in spiked subsurface soils was evaluated in this study. Kaolin and glacial till soils were selected as representative low permeability soils; both soils were spiked with 50 mg PCB per dry kilogram of soil. Activation of persulfate oxidation was necessary to achieve effective destruction of PCBs in soils. As persulfate oxidation activators, temperature and high pH were used in order to maximize PCB destruction. In addition, the effect of oxidant dose and reaction time was investigated. The optimal dose for persulfate was found to be 30% for maximum oxidation. The persulfate activation with temperature of 45°C was superior to persulfate activation with high pH (pH 12), where higher PCB destructions were observed for kaolin and glacial till soils. PCB destruction increased with reaction time, where maximum degradation was achieved after 7 days. The highest PCB destruction was achieved with temperature activation at 45°C using a dosage of 30% persulfate at pH 12 for kaolin and glacial till soils after 7 days.

The mobility of fluorescein and bromide used as tracers in packed soil columns was investigated. Five different soils were used in two application methods: soil surface application and soil incorporation, both of which simulate accepted methods of soil application of termiticides to prevent structural infestation. The breakthrough of bromide and fluorescein in column eluates were measured. The absorbance of fluorescein at 492 nm was pH dependent, and proper adjustments were made after measuring the eluate pH. Although high recoveries of bromide from the soil columns were observed, the breakthrough was different among the soil types, indicating that bromide behaves differently in different soils. Recovery of fluorescein, a weak acid, varied depending upon the pH of the soil used, and was only observed in the eluates of two of the five soils tested. Soil treated with bromide and fluorescein followed by soaking extraction showed high recovery of bromide but low recovery of fluorescein, except for in the most alkaline of the soils tested. If fluorescein is used as a conservative tracer in pesticide soil mobility studies, mobility can be underestimated in acidic soils because the active ingredient might travel more quickly than does the fluorescein.

A greenhouse experiment was performed to evaluate effectiveness of goosegrass (Eleusine indica) in phytoremediation of soil contaminated with 8,247 mg kg⁻¹ of total petroleum hydrocarbons (TPH). We determined seed germination toxicity, soil microbial viable counts, catalase activity, dehydrogenase activity (DHA), and the concentrations of TPH and 14 polycyclic aromatic hydrocarbons (PAHs) in soil and plant tissue. After 5 months, the initial level of contamination was reduced by 47% in planted soil, whereas it was only reduced by 11% in nonplanted soil. Bacterial numbers were 72 times greater in the rhizosphere treated soil than in the unvegetated treatment at the end of the study. There was no correlation between microbial counts or DHA and catalase activity, and the correlation between microbial counts and DHA was weak. Significant chemical reduction of H₂O₂, caused by the soil fabric, was observed in the determination of catalase activity. In case of vegetated treatment, 32% of PAHs was removed, but only 5% of PAHs was dissipated in the unvegetated pots. Gas chromatography/mass spectrometry analysis of plant tissue indicated that a low amount of PAHs (25.50 mg kg⁻¹ dry biomass) was detected in goosegrass roots growing in the contaminated soil, and no uptake into the shoots was occurring.

Purpose Contamination with petroleum hydrocarbons (PHC) is a global problem with environmental implications. Physico-chemical treatments can be used for soil cleanup, but they are expensive, and can have implications for soil structure and environment. Otherwise, biological remediation treatments are cost-effective and restore soil structure. Several remediation experiments have been carried out in the lab and in the field; however, there is the challenge to achieve as good or better results in the field as in the laboratory. In the ambit of a project aiming at investigating suitable biological remediation approaches for recovering a refinery contaminated soil, we present here results obtained in bioremediation trials. The approaches biostimulation and bioaugmentation were tested, in parallel, and compared with natural attenuation. For this purpose, mesocosm experiments were carried out inside the refinery area, which constitutes a real asset of this work. Methods Soil contaminated with crude oil was excavated, re-contaminated with turbine oil, homogenised and used to fill several 0.5 m³ high-density polyethylene containers. The efficiency of procedures as follows: (1) natural attenuation; (2) manual aeration; (3) biostimulation by adding (3.1) only nutrients; and (3.2) nutrients and a non-ionic surfactant; and (4) bioaugmentation in the presence of added (4.1) nutrients or (4.2) nutrients and a non-ionic surfactant were evaluated after a 9-month period of experiment. For bioaugmentation, a commercial bacterial product was used. In addition to physico-chemical characterization, initial and final soil contents in total petroleum hydrocarbons (TPH) (by Fourier transform infrared spectrophotometry) and the total number of bacteria (by total cell counts) were carried out. For TPH degradation evaluation the soil was divided in four fractions corresponding to different depths: 0-5; 5-10; 10-15; and 15-20 cm. Mean values of percentages of PHC degradation varied between 20 and 50% at surface and between 10 and 35% below 5-cm depth. Natural attenuation was as efficient as most of the tested treatments (about 30% TPH degradation) being exceeded only by bioaugmentation combined with nutrient and surfactant amendments (about 50% TPH degradation). Higher TPH degradation at surface suggests that a combination of sufficient dioxygen, propitious for aerobically degradation, with sunlight required for production of strong photochemical oxidants like ozone, contributed for enhancing degradation. Indeed, the atmosphere of the refineries is relatively rich in volatile organic compounds and nitrogen dioxide (a side-product of the combustion of residual volatile PHC released by the chimneys), which are precursors of O₃ and other photochemical oxidants produced in sunny days, which are very common in Portugal. The fact that natural attenuation was as efficient as most of the soil treatments tested was very probably a result of the presence, in the initial soil, of physiologically adapted native microorganisms, which could be efficient in degrading PHC. Conclusions A cost-effective way to reduce half-life for the degradation of PHC of contaminated soil of the refinery will be a periodic revolving of the soil, like tillage, in order to expose to the oxidative atmosphere the different layers of contaminated soil. A combination of soil revolving with bioaugmentation together with nutrients and surfactant amendments may result in an additional improvement of PHC degradation rate. However, this last procedure will raise markedly the price of the remediation treatment.

The elemental composition and bioaccessibility of trace metals have been determined in a variety of geosolids (soils, road dusts and house dusts) from an arid, coastal region (Dhahran, Saudi Arabia). Concentrations of many elements reflected those of the local geology, ascertained by analysis of desert sand. Several trace metals (e.g. Cu, Sb, Zn, Pb, Tl and Sn) were moderately enriched in both road and house dusts, reflecting external and internal (household) anthropogenic sources. For a given trace metal, bioaccessibilities, assessed using a physiologically based extraction test, were broadly similar across the range of geosolids. Median values for a simulated gastric phase ranged from less than 10% (Ba, Cu, Cr, Ni and V) to more than 50% (As, Cd, Sb, Sn and Tl), and for a subsequently simulated intestinal phase from less than 15% (Ba, Cr, Cu, Ni, V and Zn) to more than 50% (As, Cd, Sb, Tl and U). Results suggest that the levels and bioaccessibilities of trace metals in dusts from arid environments are controlled by the dilution of anthropogenic particulates by variable (but significant) proportions of fine, baseline sand.

The elevated water table (EWT) technique for preventing acid mine drainage (AMD) was tested using instrumented laboratory columns containing reactive tailings from the Louvicourt and Sigma mines, Abitibi, Quebec. The tests were performed in short (0.4 m) and long (1.4-1.7 m) columns over 400-500 days and included periodic surface recharge and subsequent monitoring of the leached drainage water. In each column, the water table depth was adjusted relative to the air entry value (AEV or ψa) of the tailings. The influence of different water table elevations was evaluated by measuring the effluent pH, as well as the concentrations of major ions including sulphate, iron, zinc, copper and lead. Provided the water table depth below the tailings surface remained less than one half of the tailings' AEV, the observed data showed that an EWT can be very effective in reducing acid mine drainage. The principal factors controlling drainage quality were the saturated hydraulic conductivity (k sat) and the air entry value (ψa) of the tailings. A lower k sat and a higher ψa in the tailings tend to increase the performance of an elevated water table by limiting drainage-induced desaturation. Mineralogical composition had relatively little effect on the hydrogeochemical evolution provided the tailings remained highly saturated (S r ≥ 90%). The results presented here indicate that an elevated water table can be an effective means for controlling the production of AMD when the design conditions are properly selected and applied.

Arsenic (As) contamination of the environment has emerged as a concerning issue recently for which phytoremediation has been suggested as a viable solution. Hydrilla verticillata (L.f.) Royle is a widely distributed rapidly growing aquatic weed possessing significant potential to accumulate As and is thus a potential candidate for the purpose of As phytoremediation. In the present study, an investigation of thiol metabolism was conducted in H. verticillata, which revealed differential effects upon exposure to arsenite [As(III)] and arsenate [As(V)]. The accumulation of arsenic was found to be higher upon exposure to As(III) than to As(V). Besides, As(III) was found to induce the activities of enzymes, such as cysteine synthase and γ-glutamylcysteine synthetase and the amounts of cysteine and glutathione (GSH) to higher levels than that observed with As(V). The activity of glutathione-S-transferase was, however, stimulated to a higher level upon exposure to As(V) than As(III). The activity of arsenate reductase was found to increase upon As(V) exposure at all concentrations and durations. In addition, a significant stimulation in the activity of phytochelatin synthase was noticed in vitro with an increase in As/GSH concentration and time of incubation. Arsenic detoxification in H. verticillata thus appeared to involve an induction of thiol synthesis and consumption in a coordinated manner, though differentially upon exposure to As(III) and As(V). The information gained through this study would help in better designing of the pilot experiment at the field level depending on the chemical composition of the contaminated water.

We evaluated the differences in the use of a quartz filter and a polytetrafluoroethylene (PTFE) filter as a first (F0)-stage filter in a four-stage filter-pack method. A four-stage filter-pack method can completely collect sulfur species (SO₂ and SO ₄ ²⁻ ), nitrate species (HNO₃ and NO ₃ ⁻ ), and ammonium species (NH₃ and NH ₄ ⁺ ) with little or no leakage irrespectively of the first-stage filter used. On the other hand, a seasonal variation was observed in the efficiency of collection between the quartz filter and the PTFE filter depending on the material to be collected. There was no seasonal variation in the efficiency of collection in sulfur species; in contrast, a clear seasonal variation was observed for the nitrate and ammonium species. As for NO ₃ ⁻ , the PTFE filter was more vulnerable than the quartz filter at air temperatures below 21°C, while the quartz filter was more vulnerable than the PTFE filter at air temperatures exceeding 21°C. A similar vulnerability for air temperature was observed for NH ₄ ⁺ , although the threshold air temperature was 23°C for NH ₄ ⁺ . Consequently, the evaporation loss of NO ₃ ⁻ would be mainly attributable to the volatilization of NH₄NO₃, although it is also partially due to the volatilization of NH₄Cl.

This study is aimed at assessing the ability of metal-resistant yeast, Candida tropicalis, to uptake cadmium from the liquid medium. The minimum inhibitory concentration of Cd²⁺ against C. tropicalis was 2,800 mg L⁻¹. The yeast also showed tolerance towards Zn²⁺ (3,100 mg L⁻¹), Ni²⁺ (3,000 mg L⁻¹), Hg²⁺ (2,400 mg L⁻¹), Cu²⁺ (2,300 mg L⁻¹), Cr⁶⁺ (2,000 mg L⁻¹), and Pb²⁺ (1,200 mg L⁻¹). The yeast isolate showed typical growth curves, but low specific rate of growth was observed in the presence of cadmium. The yeast isolate showed optimum growth at 30°C and pH 7. The metal processing ability of the isolate was determined in a medium containing 100 mg L⁻¹ of Cd²⁺. C. tropicalis could decline Cd²⁺ 57%, 69%, and 80% from the medium after 48, 96, and 144 h, respectively. C. tropicalis was also able to remove Cd²⁺ 56% and 73% from the wastewater after 6 and 12 days, respectively. Cd produced an increase in glutathione (GSH) and non-protein thiol levels by 146.15% and 59.67% at 100 mg L⁻¹ concentration, respectively. Metal tolerance and accumulation together with changes in the GSH status and non-protein thiols under Cd exposure were studied in C. tropicalis.